Fixed pointer type on MString operator=.

MString.cpp

@@ -74,7 +74,7 @@ namespace coreutils {
 	free(data);
    }
    
-   MString &MString::operator=(coreutils::MString &value) {
+   MString &MString::operator=(coreutils::MString value) {
       setSize(value.getLength());
       memcpy(data, value.getData(), value.getLength());
       length = value.getLength();